Magnetostrictive actuators of the foregoing type are generally known in the art, as disclosed for example in U.S. Pat. Nos. 4,959,567 and 5,039,894 to Ealey et al. and Teter et al., respectively. In such actuators the static magnetic bias field and the electromagnetically generated variable magnetic field have the same flux orientation parallel to the direction of strain or deformation of the active magnetostrictive component. According to the Ealey et al. patent, the magnetic pre-bias applied to the active component is adjusted to a desired stress/field characteristic point by the additive effect of concentric magnetic fields to improve actuator performance. According to the Teter et al. patent, operational performance is improved by frictional bias on the slide bearing surfaces of the active component applied by forces transverse to its direction of magnetostrictive deformation.
Because of the non-linearity between magnetostrictive strain and flux density of the concentric magnetic fields to which the active component is exposed in the foregoing actuators, excessive energy loss occurs. Also, there is considerable flux leakage caused by the interaction between the non-uniform flux in the active component and the electromagnetically generated variable magnetic field.
It is therefore an important object of the present invention to provide an improved magnetostrictive actuator of the foregoing type, wherein energy loss and flux leakage is reduced to lower power consumption, provide greater ease of control and a longer useful stroke for the active component.